Plant Availability Index by Potassium Exchange Isotherms in Selected Rice Soils of Lesser Himalayas

Abstract

Potassium (K) exchange isotherms (quantity–intensity technique, Q/I) and K values derived from the Q/I relationship provide information about soil K availability. This investigation was conducted to study Q/I parameters of K, available K extracted by 1 N ammonium acetate (NH4AOc) (exchangeable K plus solution K), K saturation percentage (K index, %), and the properties of 10 different agricultural soils. In addition, the relationship of mustard plant yield response to the K requirement test based on K exchange isotherms was investigated. The Q/I parameters included readily exchangeable K (ΔK0), specific K sites (KX), linear potential buffering capacity (PBCK), and energy of exchange of K (EK). The results of x-ray diffraction analysis of the oriented clay fractions indicated that some mixed clay minerals, illite clay minerals, along with chlorite/hydroxy interlayered vermiculite and kaolinite were present in the soils. The soil solution K activity ratio at equilibrium (AR0) ranged from 8.0 × 10−4 to 3.1 × 10−3 (mol L−1)0.5. The readily exchangeable K (ΔK0) was between 0.105 to 0.325 cmolckg−1 soil, which represented an average of 88% of the exchangeable K (Kex). The soils showed high capacities to maintain the potential of K against depletion, as they represented high linear potential buffering capacities (PBCK) [13.8 to 50.1 cmolc kg−1/(mol L−1)0.5. The EK values for the soils ranged from −3420 to −4220 calories M−1. The percentage of K saturation (K index) ranged from 0.7% to 2.2%. Analysis of variance of the dry matter (DM), K concentrations, and K uptake of mustard plants indicated that there were no significant differences among the adjusted levels of K as determined by the exchange-isotherm curve.